In a manufacturing process of semiconductor devices, a plasma etching process using a resist as a mask is widely used in order to form predetermined patterns in specific layers formed on a semiconductor wafer serving as a target substrate.
Various types of plasma etching apparatuses are used to perform the plasma etching process. Conventionally, a capacitively coupled parallel plate type plasma etching apparatus is mainly used.
In the capacitively coupled parallel plate type plasma etching apparatus, a pair of parallel plate electrodes (upper and lower electrodes) is disposed in a chamber. While a processing gas is introduced into the chamber, an RF power is applied to at least one of the electrodes to form an RF electric field between the electrodes, thereby generating a plasma of the processing gas. Accordingly, a plasma etching process is performed on specific layers of the semiconductor wafer.
Specifically, there is a plasma etching apparatus in which an appropriate plasma state is formed by applying an RF power for plasma generation having a relatively high frequency and an RF power for ion attraction having a relatively low frequency, thereby performing an etching process with high selectivity and high reproducibility (see, e.g., Japanese Patent Application Publication No. 2000-173993). In such a case, the etching process is performed by using a plasma of a processing gas in which positive ions act as dominant ions.
The recent trend of miniaturization of semiconductor devices requires High Aspect Ratio Contact (HARC) etching to obtain an aspect ratio of 20 or more. In the HARC etching, a photoresist serving as an etching mask is negatively charged and charges are neutralized on a surface to be etched at an initial step of the etching. However, when the aspect ratio increases as the etching proceeds, positive ions are accumulated at the bottom of a hole and the surface to be etched is positively charged. Accordingly, the travel direction of positive ions accelerating the etching is bent a repulsive force between the positive ions in the hole to thereby cause distortion of etched profiles. Further, less positive ions reach the bottom of the hole, thereby reducing an etching rate.